This application claims benefit of priority under 35 U.S.C. xc2xa7 119 to Japanese Patent Application No. 2001-398310, filed on Dec. 27, 2001, the entire contents of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates to a DCxe2x80x94DC converter with a plurality of transformers, and more particularly to a DCxe2x80x94DC converter composed of simple circuit structure that protects the electrical device from damages safely at the time of carrying out an abnormal test for short-circuiting or open-circuiting a transformer thereof.
2. Description of the Related Art
As shown in FIG. 1, a flyback type DCxe2x80x94DC converter having a plurality of transformers in order to increase a total capacity of the transformers has been conventionally known. According to the conventional DCxe2x80x94DC converter, primary windings T1a and T2a of transformers T1 and T2 are connected in series to a switching element Q1. One ends of secondary windings T1b and T2b of the transformers T1 and T2 are connected to anodes of diodes D1 and D2, respectively. The other ends of the secondary windings T1b and T2b are commonly connected to a negative electrode of capacitor C1. Cathodes of the diodes D1 and D2 are commonly connected to a positive electrode of the capacitor C1. Auxiliary windings T1c and T2c of the transformers T1 and T2 are connected in parallel with each other.
Further, temperature fuses TF1 and TF2 are thermally coupled to the transformers T1 and T2, and are fused at the time of reaching a specified fusing temperature. When a direct voltage is applied from a direct power source 1, a current firstly flows from the direct power source 1 through a fuse F1 and a starting resistance R1 to a capacitor C2 to increase a voltage of the capacitor C2. According to such state, a control circuit 7 is activated. A PWM signal repeating alternately a high level state and a low level state is transmitted from the control circuit 7 via the temperature fuses TF1 and TF2 to a gate of the switching element Q1.
The switching element Q1 is on-off controlled by the PWM signal outputted from the control circuit 7. Then, energy is sequentially induced from the primary windings T1a and T2a to the secondary windings T1b and T2b. The energy induced on the secondary windings T1b and T2b is rectified and smoothed by the diodes D1, D2 and the capacitor C1, and then is supplied to a load 4 as an output voltage. At the same time, a voltage generated at both ends of the capacitor C1 is detected by a voltage detection circuit 10 to generate a detection signal. The detection signal is fed back to the control circuit 7 and then the control circuit 7 controls an on period of the switching element Q1 in order to supply a certain output voltage to the load 4.
There are operational tests for DCxe2x80x94DC converter. One of the operational tests is an abnormal test for confirming safety of device by short-circuiting or open-circuiting a transformer thereof. As shown in FIG. 2, the abnormal test has four test items. It will be described how the temperature fuse protects the electrical device from damages in the abnormal test.
(1) Short of Primary Winding
As shown in FIG. 2(1), a switch SW1as is open in advance and is connected in parallel to the primary winding T1a of the transformer T1. When the switch SW1as is closed during an operation of the DCxe2x80x94DC converter, an inductance component L of the secondary winding T1b of the transformer T1 is minimized. In such condition, because energy is not induced from the primary winding T1a to the secondary winding T1b, a power supplied to the load 4 is generated only by the transformer T2. This gradually increases a temperature of the transformer T2 during the operation of the DCxe2x80x94DC converter. The increased temperature of the transformer T2 causes a temperature of the temperature fuse TF2 coupled thermally to the transformer T2 to reach a specified fusing temperature. At the specified fusing temperature, the temperature fuse TF2 is fused. When the temperature fuse TF2 is fused, a PWM signal transmitted from the control circuit 7 to the switching element Q1 is interrupted, stopping an operation of the switching element Q1. This cuts off current flow supplied to the transformer T2. As a result, an increase in temperature of the transformer T2 is stopped. The above-described operations can prevent the DCxe2x80x94DC converter from firing or smoking caused by the increased temperature of itself. Therefore, the electrical device is protected from damages. Incidentally, it should be noted that the fuse F1 dose not exert any influences on the short test for the primary winding because the temperature fuse TF2 is always fused prior to the fuse F1 in this short test for absence of excess current.
(2) Short of Secondary Winding
As shown in FIG. 2(2), a switch SW1bs is open in advance and is connected in parallel to the secondary winding T1b of the transformer T1. When the switch SW1bs is closed during an operation of the DCxe2x80x94DC converter, an inductance component L of the primary winding T1a of the transformer T1 is minimized. In such condition, because energy is not induced from the primary winding T1a to the secondary winding T1b, a power supplied to the load 4 is generated only by the transformer T2. Similarly to the short of the primary winding, this gradually increases a temperature of the transformer T2 during the operation of the DCxe2x80x94DC converter. The increased temperature of the transformer T2 causes a temperature of the temperature fuse TF2 coupled thermally to the transformer T2 to reach a specified fusing temperature. At the specified fusing temperature, the temperature fuse TF2 is fused. When the temperature fuse TF2 is fused, a PWM signal transmitted from the control circuit 7 to the switching element Q1 is interrupted, stopping an operation of the switching element Q1. This cuts off current flow supplied to the transformer T2. As a result, an increase in temperature of the transformer T2 is stopped. The above-described operations can prevent the DCxe2x80x94DC converter from firing or smoking caused by the increased temperature of itself. Therefore, the electrical device is protected from damages. Incidentally, it should be noted that the fuse F1 does not exert any influences upon the short test for the secondary winding because the temperature fuse TF2 is always fused prior to the fuse F1 in this short test for absence of excess current.
(3) Open of Primary Winding
As shown in FIG. 2(3), a switch SW1ao is closed in advance and is connected in series to the primary winding T1a of the transformer T1. When the switch SW1ao is opened during an operation of the DCxe2x80x94DC converter, a current flowing through the primary windings T1a and T2a of the transformers T1 and T2 is cut off. As a result, power supply to the load 4 is stopped.
(4) Open of Secondary Winding
As shown in FIG. 2(4), a switch SW1bo is closed in advance and is connected in series to the secondary winding T1b of the transformer T1. When the switch SW1bo is opened during an operation of the DCxe2x80x94DC converter, a power supplied to the load 4 is generated only by the transformer T2. This gradually increases a temperature of the transformer T2 during the operation of the DCxe2x80x94DC converter. The increased temperature of the transformer T2 causes a temperature of the temperature fuse TF2 coupled thermally to the transformer T2 to reach a specified fusing temperature. At the specified fusing temperature, the temperature fuse TF2 is fused. When the temperature fuse TF2 is fused, a PWM signal transmitted from the control circuit 7 to the switching element Q1 is interrupted, stopping an operation of the switching element Q1. This cuts off current flow supplied to the transformer T2. As a result, an increase in temperature of the transformer T2 is also stopped. The above-described operations can prevent the DCxe2x80x94DC converter from firing or smoking caused by the increased temperature of itself. Therefore, the electrical device is protected from damages. Incidentally, it should be noted that the fuse F1 does not exert any influences upon the open test for the secondary winding because the temperature fuse TF2 is always fused prior to the fuse F1 in this open test for absence of excess current.
The abnormal test items (1) through (4) are implemented with respect to the transformer T1. If the same test items are carried out upon the transformer T2, the same results can be obtained. As described above, by means of the abnormal test short-circuiting or open-circuiting a transformer of the DCxe2x80x94DC converter, it is possible to confirm whether the temperature fuse stops an operation of the switching element Q1 to protect electrical device from damages safely at the time of abnormal condition on the DCxe2x80x94DC converter or not.
In the above-described abnormal test items (1), (2) and (4), however, an operation of the switching element Q1 continues for a while by using a transformer that is not short-circuited or open-circuited. Specifically, the switching element Q1 continues to operate until an increased temperature of the transformer fuses a temperature fuse to interrupt a PWM signal. Therefore, there are questions about reliability of the electrical device including the conventional DCxe2x80x94DC converter in abnormal condition. Further, it is necessary to provide transformers with heat-resistance and the number of temperature fuses being equal to the number of the transformers in the electrical device. Accordingly, the production costs of this device are increased. Moreover, a large space for mounting a number of the electrical components refuses compactness of the electrical device.
Accordingly, it is desirable to provide a DCxe2x80x94DC converter composed of simple circuit structure, which can stop an operation of switching element in a short time for safely protecting the electrical device from damages in an abnormal test.
An object of the present invention is to provide a DCxe2x80x94DC converter with a plurality of transformers composed of simple circuit structure, which can stop an operation of switching element in a short time in order to protect electrical device from damages at the time of carrying out an abnormal test for confirming safety of device by short-circuiting or open-circuiting a transformer thereof.
In order to accomplish the aforementioned object, the present invention provides a DCxe2x80x94DC converter that converts a direct voltage inputted from a direct power source into a predetermined direct voltage by controlling an on period of switching element and outputs a converted voltage, the DCxe2x80x94DC converter comprising an overcurrent cut-off means connected in series to the direct power source; primary windings of two or more transformers connected in series to the overcurrent cut-off means; secondary windings of the two or more transformers connected in parallel with each other; and auxiliary windings of the two or more transformers connected in parallel with each other.
According to the present invention, when a short test is carried out for the primary windings or the secondary windings of two or more transformers, the overcurrent cut-off cuts off an overcurrent flow to stop an operation of the switching element in a short time. This can safely protect the electrical device from damages.
In order to accomplish the aforementioned object, the present invention provides a DCxe2x80x94DC converter that converts a direct voltage inputted from a direct power source into another direct voltage and outputs a converted voltage, the DCxe2x80x94DC converter comprising an overcurrent cut-off means connected in series to the direct power source and cutting off an overcurrent flow; primary windings of two or more transformers connected in series to the overcurrent cut-off means and connected in series with each other; a switching element connected in series to the primary windings of the two or more transformers; secondary windings of the two or more transformers connected in parallel with each other; a rectifying and smoothing circuit for rectifying and smoothing a voltage which is induced by the secondary windings of the two or more transformers; a first short means for short-circuiting a transformer, that is connected in parallel to a primary winding of first short transformer selected among the two or more transformers; and a second short means for short-circuiting a transformer, that is connected in parallel to a secondary winding of second short transformer selected among the two or more transformers, wherein when carried out by using the first or second short means is a short test for confirming safety of device, the overcurrent cut-off means cuts off an overcurrent flow generated by short-circuit of the first or second short transformer.
According to the present invention, when the short test is carried out by using the first or second short means, the overcurrent cut-off means cuts off an overcurrent flow generated by short-circuit of the first or second short transformer to stop the operation of the switching element. Therefore, even if a protection circuit such as a conventional temperature fuse is not provided, an operation of the switching element can be stopped in a short time, which can contribute to compactness of the electrical device and reduction in production costs.
In a preferred embodiment of the invention, each of the first and second short means is formed of switch, the switch is set to be open in advance and then is closed at a time of carrying out the short test.
According to this embodiment, a transformer can be short-circuited by a simple structure utilizing a switch.
In a preferred embodiment of the invention, the overcurrent cut-off means is formed of fuse.
According to this embodiment, an overcurrent flow can be cut off by a simple structure utilizing a fuse.
In order to accomplish the aforementioned object, the present invention provides a DCxe2x80x94DC converter that converts a direct voltage inputted from a direct power source into another direct voltage and outputs a converted voltage, the DCxe2x80x94DC converter comprising primary windings of two or more transformers connected in series to the direct power source and connected in series with each other; a switching element connected in series to the primary windings of the two or more transformers; secondary windings of the two or more transformers connected in parallel with each other; a first rectifying and smoothing circuit for rectifying and smoothing a voltage which is induced by the secondary windings of the two or more transformers; auxiliary windings of the two or more transformers coupled magnetically to the primary windings of the two or more transformers and connected in parallel with each other; a second rectifying and smoothing circuit for rectifying and smoothing a voltage which is induced by the auxiliary windings of the two or more transformers; an overvoltage detection circuit that outputs a stop signal if a voltage outputted from the second rectifying and smoothing circuit is larger than a reference voltage; a control circuit that stops an operation of the switching element in response to the stop signal outputted from the overvoltage detection circuit; a first open means for open-circuiting a transformer, that is connected in series to a primary winding of first open transformer selected among the two or more transformers; and a second open means for open-circuiting a transformer, that is connected in series to a secondary winding of second open transformer selected among the two or more transformers, wherein when carried out by using the first or second open means is an open test for confirming safety of device, an operation of the switching element is stopped.
According to the present invention, when the open test is carried out by using the first or second open means, the operation of the switching element can be stopped in a short time. Therefore, the electrical device can be safely protected from damages.
In a preferred embodiment of the invention, each of the first and second open means is formed of switch, the switch is set to be closed in advance and then is opened at a time of carrying out the open test.
According to this embodiment, a transformer can be open-circuited by a simple structure utilizing a switch.
In a preferred embodiment of the invention, when the open test is carried out by using the first open means, the first open means cuts off a flow of current so as to stop an operation of the switching element, and when the open test is carried out by using the second open means, the stop signal is outputted from the control circuit in response to a surge voltage, which is generated on the auxiliary winding due to open of the second open transformer, so as to stop an operation of the switching element.
According to the present embodiment, when the open test is carried out by using the first open means, the first open means cuts off a flow of current to stop the operation of the switching element. When the open test is carried out by using the second open means, a stop signal is outputted from the control circuit in response to a surge voltage, which is generated on the auxiliary winding due to open-circuit of the second open transformer, to stop the operation of the switching element. Therefore, even if a protection circuit such as a conventional temperature fuse is not provided, the operation of the switching element can be stopped in a short time, which can contribute to compactness of the electrical device and reduction in production costs.
In order to accomplish the aforementioned object, the present invention provides a DCxe2x80x94DC converter that converts a direct voltage inputted from a direct power source into another direct voltage and outputs a converted voltage, the DCxe2x80x94DC converter comprising an overcurrent cut-off means for cutting off an overcurrent flow, that is connected in series to the direct power source; primary windings of two or more transformers connected in series to the overcurrent cut-off means and connected in series with each other; a switching element connected in series to the primary windings of the two or more transformers; secondary windings of the two or more transformers connected in parallel with each other; a first rectifying and smoothing circuit for rectifying and smoothing a voltage which is induced by the secondary windings of the two or more transformers; a voltage detection circuit outputting a feedback signal in response to error voltage between a first reference voltage and the smooth direct voltage outputted from the first rectifying and smoothing circuit; auxiliary windings of the two or more transformers coupled magnetically to the primary windings of the two or more transformers and connected in parallel with each other; a second rectifying and smoothing circuit for rectifying and smoothing a voltage induced by the auxiliary windings of the two or more transformers; an overvoltage detection circuit that outputs a stop signal if a voltage outputted from the second rectifying and smoothing circuit is larger than a second reference voltage; a control circuit that controls an on period of the switching element in response to the feedback signal outputted from the voltage detection circuit and stops the operation of the switching element according to the stop signal outputted from the overvoltage detection circuit; a first short means for short-circuiting a transformer, that is connected in parallel to a primary winding of first short transformer selected among the two or more transformers; a second short means for short-circuiting a transformer, that is connected in parallel to a secondary winding of second short transformer selected among the two or more transformers; a first open means for open-circuiting a transformer, that is connected in series to a primary winding of first open transformer selected among the two or more transformers; and a second open means for open-circuiting a transformer, that is connected in series to a secondary winding of second open transformer selected among the two or more transformers, wherein when carried out by using the first or second short means is a short test for confirming safety of device or carried out by using the first or second open means is an opne test for confirming safety of device, the operation of the switching element is stopped.
According to the present invention, when the short test is carried out by using the first or second short means or the open test is carried out by using the first or second open means, the operation of the switching element can be stopped in a short time. Therefore, the electrical device can be safely protected from damages.
In a preferred embodiment of the invention, each of the first and second short means is formed of switch, the switch is set to be open in advance and then is closed at a time of carrying out the short test, each of the first and second open means is formed of switch, the switch is set to be closed in advance and then is opened at a time of carrying out the open test, and the overcurrent cut-off means is formed of fuse.
According to this embodiment, a transformer can be short-circuited or open-circuited by a simple structure utilizing a switch. Further, an overcurrent flow can be cut off by a simple structure utilizing a fuse.
In a preferred embodiment of the invention, when the short test is carried out by using the first or second short means, the overcurrent cut-off means cuts off an overcurrent flow, which is generated by short of the first or second short transformer, so as to stop the operation of the switching element, when the open test is carried out by using the first open means, the first open means cuts off a flow of current so as to stop the operation of the switching element, and when the open test is carried out by using the second open means, the stop signal is outputted from the control circuit in response to a surge voltage, which is generated on the auxiliary winding due to open of the second open transformer, so as to stop the operation of the switching element.
According to this embodiment, when the short test is carried out by using the first or second short means, the overcurrent cut-off means cuts off an overcurrent flow, which is generated by short-circuit of the first or second short transformer, to stop the operation of the switching element. Further, when the open test is carried out upon this DCxe2x80x94DC converter by using the first open means, the first open means cuts off a flow of current to stop the operation of the switching element. When the open test is carried out by using the second open means, a stop signal is outputted from the control circuit in response to a surge voltage, which is generated at the auxiliary winding due to open of the second open transformer, to stop the operation of the switching element. Therefore, even if a protection circuit such as a conventional temperature fuse is not provided, the operation of the switching element can be stopped, which can contribute to compactness of the electrical device and reduction in production costs.